Electrolytic hydrodimerization alpha, beta-olefinic nitriles



United States Patent 3,193,481 ELEQTROLYTM HYDRODHMERTZATION a,,8-0LEFENIC NKTRILES Manuel M. Baizer, St. Louis, Mo., assignor to Monsanto Company, a corporation of Delaware No Drawing. li iied Dec. 26, 1963, Ser. No. 333,647

23 Claims. ((11. 204-43) This application is a continuation-in-part of my copending application Serial No. 75,130, filed December 12, 1960, and now forfeited; my copending application Serial No. 145,482, filed October 16, 1961, and now abandoned; my copending application Serial No. 189,072, filed April 20, 1962; and my copending application Serial No. 228,740, filed October 5, 1962, and now abandoned.

This invention relates to the manufacture of polyfunctional compounds and more particularly provides a new and valuable electrolytic process for the hydrodimeriza tion of aliphatic alpha,beta-mono-olefinic nitriles.

The present invention is concerned with the hydrodimerization, i.e., the reductive dimerization, of certain olefinic compounds to obtain saturated dimers thereof. A general object of the invention is the provision of an improved process for the preparation of alkane dior tetra-nitriles. Another object is the provision of a technically feasible, electrolytic process for the conversion of aliphatic alpha,beta-olefinic nitriles to parafiinic dinitriles. Still another object is the electrolytic conversion of aliphatic alpha,beta-olefinic dinitriles to paraftinic tetranitriles. An important object of the invention is the provision of an electrolytic process of converting aliphatic alpha,beta-mono-olefinic nitriles to obtain good yields of the saturated dimers thereof rather than a preponderance of hydrogenated monomers and/ or complex organometallic compounds. A very important objective of the invention is the provision of an electrolytic process wherein there are obtained better than 50% and even better than 80% up to substantially theoretical yields of hydrodimerization products of the aliphatic alpha,beta-mono-olefinic nitriles employed in the process.

These and other objects of the invention hereinafter described are provided by the present process for conducting the hydrodimerization of an aliphatic alpha,beta mono-oleiinic nitrile of, for example, from 3 to 8 carbon atoms, which comprises subjecting to electrolysis, in contact with a cathode, a solution of the olefinic compound in an aqueous electrolyte under non-polymerizing condi tions such that the desired hydrodimer is obtained and recovered in appreciable yield. It is desirable to employ fairly concentrated solutions in order to minimize undesired reactions of intermediate ions with the water of the electrolyte. The average amount of the nitrile reactants will be at least about by weight of the catholyte, and preferably at least 10% by weight or more. The process is characterized by fairly high concentrations of salts in the catholyte, constituting at least 5% by weight of the catholyte and usually constituting 30% or more by weight of the total amount of salt and water in the catholyte, in order to obtain the desired solubility of the olefinic compounds and the desired conductivity.

The salt concentration has an important bearing upon the results obtained. When the salts are hydrotropic, high concentrations contribute to solubility of the alpha, beta-olefinic nitriles, making it possible to utilize higher concentrations of the nitriles. centration of salt cations in some way affects the course of the reaction and results in higher yields of hydrodimers at the expense of products simple reduction products. The process of the present invention is carried out utilizing a supporting electrolyte as understood by those in the art, i.e., electrolyte capable of carrying current but But beyond this, the con- 3,193,481 Patented July 6, 1965 not discharging under the electrolysis conditions, but with the requirement that the supporting electrolyte be a salt and that it constitute at least 5% by weight of the solution electrolyzed. The requirements of supporting electrolytes are well understood by those skilled in the art and they will be able to select such electrolytes and utilize them in the proper concentrations in view of the teaching herein as to catholyte required for hydrodimerizations of alpha,beta-olefinic nitriles, and salt concentrations essential to such hydrodimerizations. As the hydrodimerization of acrylonitrile, for example, proceeds at the cathode voltages which can vary from, say about l.8 to about -2.1 volts (vs. saturated calomel electrode), depending somewhat upon conditions, any electrolyte salts not subject to substantial discharge at less negative conditions can .be employed, and to some extent those discharging at about 1.6 to 1.7 volts (vs. saturated calomel electrode). Thus, extensive classes of suitable electrolyte salts are available for use. The salts can be organic or inorganic, or mixtures of such, and composed of simple cations and anions or very large complex cations and anions. The term salts is employed herein in its generally recognized sense to indicate a compound composed of a cation and an anion, such as produced by reaction of an acid with a base.

It is preferred that the salts employed herein have the properties of that class of salts recognized as hydrotropic, i.e., as promoting the solubility of organic compounds in water. Various organic sulfonates, alkyl sulfates, etc., have hydrotropic eliects. In this application, any salt which increases the solubility of olefinic nitriles in Water is considered hydrotropic.

Some olefinic compounds are subject to polymerization or other side reactions if the electrolyte is acidic, or excessively alkaline, and it will be desirable in such cases to conduct the reductive coupling in solutions which are not overly acidic and also in some cases below a pH at which undesirable side reactions occur, e.g., below about 12. To minimize polymerization, simple reduction of the olefinic bond and other side reactions, the pH is usually maintained in the range of about 3 to about 12, preferably 6 to 9.5. In addition, when the catholyte during electrolysis is acidic, it will generally be advisable to conduct the electrolysis under conditions which inhibit polymerization of the reactants involved or in the presence of a polymerization inhibitor, for example, in an atmosphere containing sui'licient oxygen to inhibit the polymerization in question, or in the presence or" inhibi tors effective for inhibiting free radical polymerization. Classes of inhibitors for inhibiting free radical polymerizations are well known, e.g., such inhibitors as hydroquinone, p-t-butyl catechol, quinone, p-nitrosodimethylani line, di-t-butyl hydroquinone, 2,5-dihydroxy-1,4-benzoquinone, 1,4-naphthoquinone, chloranil, 9,10-phenanthraquinone, 4-amino-1-naphthol, etc., are suitable. The present process will ordinarily be conducted in the absence of free radical polymerization catalysts or materials which will form polymerization catalysts under the electrolysis conditions, although their presence is not necessarily undesirable if polymerization is sufiiciently inhibited or conditions are otherwise such that polymerization will not occur. The inhibitors are ordinarily used in small amounts, e.g., less than 1% by weight based on the olefinic nitrile, for example 0.01% by weight based on the olefinic nitrile, but can be used in larger amounts such as up to 5% or more by weight, based on the olefinic nitrile.

Even though suit-able inhibitors are employed, the yields are generally markedly better under conditions which are not greatly acidic. However, the deleterious eiiects of acidity can be to some extent overcome by use of fairly concentration of dissolved olefinic nitrile than is required at room temperature. Because the extent of hydrodimerization appears to be related to the concentration of the olefinic nitrile in the electrolysis solution, when the electrolysis is to be conducted at room temperature, the olefinic nitrile is advantageously added to a saturated aqueous solution of the salt in order to obtain thereby as high a concentration as possible of the dissolved olefinic nitrile. When the electrolysis is to be conducted at a temperature of above room temperature, high concentrations of olefinic nitrile can be attained with unsaturated solutions of the salt, i.e., the salt may be as low as 30% by weight of the electrolysis solution. Concentration of the olefinic nitrile in the electrolysis solution may also be increased by using a mixture of water and a polar solvent, e.g., acetonitrile, dioxane, ethylene glycol, dimethylformamide, dimethylacetamide, ethanol or isopropanol, together with the aromatic salt.

An electrolytic cell preferably having a cathode of high hydrogen overvoltage is charged with the thus prepared solution and an electric current is passed through the cell to elfect the hydrodimerization reaction. Depending upon the concentration of the olefinic nitrile and upon the hydrogen ion concentration of the solution, there may or may not be formed products other than the saturated dimer. Thus, when working with concentrations of olefinic nitrile which are less than or from 10 to by weight of the solution, there may be formed, in addition to the hydrodimerization product, compounds such as the reduced monomers or other condensation products. With acrylonitrile, for example, propionitrile and/ or bis(2-cyanoethyl)ether may thus be obtained as by-products. The hydrogen ion concentration of the solution will ordinarily be such as to give a pH of 7 or higher, as neutral or mildly alkaline solutions are ordinarily preferred. Many of the olefinic nitriles tend to polymerize when electrolyzed in strongly acidic solution, such as solutions of mineral acids, and it is desirable or almost necessary in such cases to avoid excesive acidity, making it desirable to operate at pHs above about 5 or 6, such as provided by solutions of salts of strong bases. Moreover, the hydrogen ion has a cathode discharge potential of about 1.5 volts, making it desirable to avoid high concentrations of hydrogen ion in the catholyte if the reductive coupling occurs at similar or more negative cathode potentials. The reductive couplings can suitably be conducted at pHs higher than those at which substantial polymerization of olefinic compound occurs, or higher than pHs at which there is undue generation of hydrogen, for example, at pHs higher than those at which more than half the current is expended in discharging hydrogen ions. The pI-Is referred to are those obtaining in the bulk of the catholyte solution, such as determinable by a pH meter on a sample of the catholyte removed from the cell. The electrolysis in effect generates acid at the anode and base at the cathode; it will be recognized that in an undivided cell the pH in the immediate vicinity of the cathode may differ considerably from that near the anode, particularly if good stirring is not employed. To some extent the effects of acidity can be counteracted by high current density to cause more rapid generation of hydroxyl ions.

However, high current densities also require good stirring or turbulence to move the reactants to the cathode.

During electrolysis in a divided cell, alkalinity increases in the catholyte. However, the anolyte becomes acidic. When a porous diaphragm is used to separate the catholyte from the anolyte, the alkalinity of the catholyte will depend upon the rate of diffusion of acid from the anolyte through the porous barrier. Control of alkalinity in the catholyte, when employing a diaphragm, may thus be realized by purposely leaking acid from the anolyte into the catholyte. It can also be achieved, of course, by extraneous addition to the catholyte of an acid material, e.g.,

glacial acetic acid, phosphoric acid or p-toluenesulfonic acid. Alkalinity may also be controlled, whether or not a diaphragm is used in the cell, by employing buffer systems of cations which will maintain the pH range while not reacting at the reaction conditions. Control of alkalinity becomes particularly necessary if the eelctrolytic hydrodimerization is carried to a high conversion, or if it is conducted in a continuous manner with continuous or intermittent addition of nitrile and removal of product, while the electrolyte itself stays in the cell or is recycled to the cell. While a successful hydrodimerization could be successfully conducted for some period of time without provisions to counteract the alkalinity, it is apparent that eventually the build-up of hydroxyl ions in the catholyte of a divided cell would be such as to cause undesirable sidereactions to predominate. Therefore, for high conversion or continuous procedures it is necessary to employ a means for controlling the alkalinity. When the olefinic compound is acrylonitrile, it will be desirable to maintain the pH at values no greater than 9.5 or 10 in order to avoid or substantially minimize cyanoethylation. Otherwise, substantial quantities of bis(beta-cyanoethyl)ether are obtained and conversion to adiponitrile is correspondingly reduced. Similarly, when other olefinic nitriles are employed, it will be desirable to maintain the pH low enough to substantially minimize addition of water to the double bond. Good agitation or turbulence counteracts excess alkalinity to some extent, by minimizing local concentrations of hydroxyl ions at the cathode, making it possible to operate efiiciently at higher bulk pHs. Moreover, good agitation maintains a suitable nitrile concentration near the cathode and keeps the electrolysis rate and use of high current densities from being unnecessarily limited by slow diffusion rates. Agitation as used herein is intended to include movement of the electrolysis medium whether resulting from stirring, beating, vibration, pumping or bubbling fluids through the medium, circulation of the medium itself, with or without bathing, and various other means of causing currents in the electrolyte medium or admixture of the components thereof.

The term consisting essentially of as employed herein with respect to the solutions electrolyzed is intended to leave the solutions open to addition of other components which do not change the basic nature of the solutions with respect to the electrolytic hydrodimerization process being conducted therein.

When a divided cell is employed, it will often be desirable to use an acid as the anolyte, any acid being suitable, particularly dilute mineral acids such as sulfuric or phosphoric acid. Hydrochloric acid can be employed but would have the disadvantage of generating chlorine at the anode, and of being more corrosive with respect to some anode materials. If desired, a salt solution can be used as anolyte, those useful as catholyte also being suitable as anolyte, although there are many other salt solutions suitable for such use. It will be recognized that the descriptions of the catholyte or acrylonitrile solutions herein apply to the solutions, regardless of whether they are in an undivided cell serving as both catholyte and anolyte, or are in the cathode-containing portion of a divided cell. Conversely, when a divided cell is employed, the various descriptions of the catholyte do not necessarily apply to the anolyte, as the olefinic nitrile is not ordinarily present in the anolyte and the character of the anolyte is not of primary importance to the hydrodimerization reaction which is occurring in the catholyte. As a practical matter, to obtain good yields in the operation of a continuous process over a matter of days or weeks, it may be necessary to employ a divided cell to avoid or minimize interfering reactions, such as resulting from generation of hydrogen ions at the anode or resulting in deposition of various salt materials on the anode. Moreover, many suitable catholyte salts are subject to degradation if permitted to contact the anode, making it advantageous to employ mineral acids as the anolyte in a divided cell.

In the past various electrolysis reactions for reducing or otherwise altering organic compounds have been known. In general, however, such reactions have had the disadvantage of being of small scale and low velocity and requiring careful control of many conditions. Quite often such reactions could not be scaled-up? by using high current densities to give practical production rates and therefore remained laboratory curiosities. In contrast, the present process operates very eifectively at current densities of greater than 10 amperes/square decim'eter of cathode surface, and the most suitable densities may be in the range of to to 40 or 50 amperes/ square decimeter and higher, even up to 100 or more amperes/square decimete'r, and it is further possible to use cells having a large effective electrode area, whether in a single set of electrodes or in reasons of economics and to make practical useof such current densities without necessitating prohibitively high cell voltages, it is essential to have fairly low resistance in the cell as obtainable by utilizing fairly high concentrations of the electrolyte salt and a relatively narrow gap between the electrodes, e.g., no more than oneralf inch, and preferably of the order of one-fourth inch or smaller. Applied voltages of 5 to 20 volts for current densities of 15 to 40 amperes/dm. are suitable, and it is preferable, in this range as well as at higher densities that the applied voltage have a numerical value no greater than one-half the numerical value of the current density (in amperes/dm. Various power sources are suitable for use in the present invention, particularly any efficient sources of dissolved olefinic nitrile, the amine and quaternary ammonium salts are generally suitable, especially those of sul fonic-and alkyl sulfuric acids. Such salts can be .the saturated aliphatic amine salts or heterocy clic amine salts, e.g., the.rnono-, di-, or trialkyl-amine salts, or the mono-, dior trialkanolamine salts, or the piperidine, pyrrolidine or morpholine salts, e.g., the ethylamine, dimethylamine or triisopropylamine salts of various acids, especially'various sulfonic acids. Especially preferred are aliphatic and heterocyclic quaternary ammonium salts, i.e., the tetraalkylammonium or the tetraalkanolammonium salts or mixed alkyl alkanol ammonium salts such as the alkyltrialkanolammonium, the dialkyldialkanolammonium, the .alkanoltrialkylamrnonium or the N- het erocyclic N-alkyl ammonium salts of sulfonic or other suitable acids. The saturated laliphaticor .heterocyclic V quaternary ammonium cations in general have suitably of direct current, and, if desired, various known means of varying the applied potential to regulate the current density 835,631 issued May 20, 1958, the disclosure of which is incorporated herein, by'reference. If desired alternating current can be superimposed on the direct current applied to the cell.

Materials'suitable for constructing the electrolysis cell employed in the present process are well known to those skilled in the art. The electrodes can be of any suitable cathode and anode material. The anode may be of virtually any conductor, although it will usually be advantageous to employ those that are relatively inert or attacked or corroded only slowly by the electrolytes; suitable anodes are, for example, platinum, carbon, gold, nickel, nickel silicide, Duriron, lead, and lead-antimony and leadcopper alloys, and alloys of various of the foregoing and other metal. I i 1 Any suitable material can be employed as cathode, various metals and alloys being. known to the art. It is generally advantageous to employ metals ,of fairly high hydrogen overvoltage in order to promote' current efficiency and minimize generation of hydrogen during the electrolysis. In general it will be desirable to employ cathods having overvoltages at least about as great as that of copper, as determined in a 2N sulfuric acid solution at current density of l milliamp./square centimeter (Carman, Chemical Constitution and Properties of Engineering Materials, Edward Arnold and Co., London, 1949, page 290). Suitable electrode materials include, for example, mercury, cadmium, tin, zinc, bismuth, lead, graphite, aluminum, nickel, etc., in general those of higher overvoltage being preferred-although those oflower hydrogen overvoltage can also be employed,.even if they cause generation of hydrogen under the electrolysis conditions, as is the case with stainless steel and other; elec- U igh cathode discharge potentials for use in the present invention and readily form salts having suitably high water solubilitywith anions suitable for use in the electrolytes employed in the present invention. The saturated, aliphatic or heterocyClic quaternary ammonium salts are therefore in general well adapted to dissolving high amounts of olefinicnitriles in their aqueous solutions and to effecting reductive couplings of such olefinic compounds. ItQ-is understood, of course, that it is undesirable that the ammonium groups contain any reactive groups which might interfere to some extent with the reductive coupling reaction. In this connection it shouldtbe noted that aromatic unsaturation as such does not interfere as benzyl substituted ammonium cations can be employed; (as also can aryl. sulfonate anions).

Among the anions useful in the electrolytes, the aryl and alkaryl sulfonic acids are especially suitable, for example, salts of the following acids: benzenesulfonic acid, 0-, mor p-toluenesulfonic acid, 0-, m-, or p-ethylbenzeuesulfonic acid, 0-, m-, or p-cumenesulfonic acid, 0-, m-, or p-tertamylbenzenesulfonicacid, o-, m-, or p-hexylbenzenesulfonic acid, o-xylene-4-sulfonic acid, p-xylene-Z-sulfonic acid, .m-xylene-4 or 5 sulfonic acid, mesitylene-Z- sulfonic acid, durene-3-sulfonic acid, pentamethylbenzene- 'sulfonic acid, o-dip'ropylbenzene-4-sulfonic acid, alpha- .or beta-naphthalenesulfonic acid, 0-, mor p-biphenylsulfonic acid, and alpha methyl beta-naphthalenesulfonic acid. Alkali metal salts are useful in the present invention with certain limitations, and the alkali metal salts of such sulfonic acids can be employed, i.e., the sodium, potassium, lithium, cesium or rubidium salts such as sodium trodes of lower hydrogen overvoltage. It will be realized that overvoltage can vary with the type of surface and prior history of the metal as well as with other. factors;

- therefore the term overvoltage asused herein with respect benz'ene-sulfonate, potassium p-toluenesulfonate, lithium o-biphenylsulfonate, rubidium beta-naphthalene-sulfonate, cesium p-ethylbenzenesulfonate, sodium o-Xylene-3-sulfonate, or potassium pentamethylbenzene-sulfonate. The

salts of such sulfonic acids may also .bethe saturated,

aliphatic amine or heterocyclic amine salts, e. g., the mono-,

dior trialkyamine salts, or the mono-, dior trialkanolamine salts, or the piperidine, pyrrolidine, or morpholine salts, e.g., the ethylamine, dimethylarnine or triisopropylaminesalt of benzenesulfonic acid or of o-, por mtoluenesulfonic acid; the isopropanolamine, dibutanolamine or triethanolamine salt or o-, por m-toluenesulfonic acid or of 0-, p-or m-biphenylsulfonic acid, the

piperidine' salt of alphaor beta-naphthalenesulfonic acid or of the cumene-sulfonic acids; the pyrrolidine salt substituted ammonium hydroxide with the sulfonic acid or with an acyl halide thereof. For example, by reaction of a sulfonic acid such as p-toluenesulfonic acid with a tetraalkylammonium hydroxide such as tetraethylammonium hydroxide there is obtained tetraethylammonium p-toluenesulfonate, use of which in the presently provided process has been found to give very good results. Other presently useful quaternary ammonium sulfonates are, e.g., tetraethylammonium o-, or m-toluenesulfonate or benzenesulfonate; tetraethylammonium mor p-cumenesulfonate, or o-, m-, or p-ethylbenzenesulfonate, tetramethylammonium benzenesulfonate, or o-, mor p-toluenesulfonate; N,N-di-methyl-piperidinium o-, mor p-toluenesulfonate or o-, mor p-biphenylsulfonate; tetrabutylammonium alphaor beta-naphthalenesulfonate or o-, mor p-toluenesulfonate; tetrapropylammonium o-, mor p-amylbenzenesulfonate or alphaethyl-beta-naphthalene sulfonate; tetraethanolammonium o-, mor p-cumenesulfonate or o-, mor p-toluenesulfonate; tetrabutanolammonium benzenesulfonate or pxylene-3-sulfonate; tetrapentylammonium o-, mor ptoluenesulfonate or o-, mor p-hexylbenzenesulfonate, tetrapentanolammonium p-cymene-S-sulfonate or benzenesulfonate; methyltriethylammonium o-, m or p-toluenesulfonate or mesitylene-Z-sulfonate; trimethylethylammonium o-xylene-4-sulfonate or o-, m-, or p-toluenesulfonate; triethylpentylammonium alphaor beta-naphthalenesulfonate or o-, mor p-butylbenzenesulfonate, triethylethanolammonium benzenesnlfonate or o-, mor p-toluenesulfonate; N,N-di-ethylpiperidinium or N-methylpyrrolidinium, o-, mor p-hexylbenzenesulfonate or o-, m or p-toluenesulfonate, N,N-di-isopropyl or N,N-dibutylmorpholinium o-, mor p-toluenesulfonate or o-, mor p-biphenylsulfonate, etc.

The tetraalkylammonium salts of the aryl or alkarylsulfonic acids are generally preferred for use as the salt constituents of the electrolysis solution because the electrolyses in the tetraalkylammonium sulfonates are exclusively electrochemical processes. Employing the same concentration of alpha,beta-olefinic nitrile, the same cathodic voltage, but using the alkali metal sulfonates instead of the tetraalkylammonium sulfonates, yields of hydrodimerization products are markedly lower than those obtained with tetraalkylammonium sulfonates. This is true even when there is present in the catholyte the high concentration of olefinic compound which can be attained by employing with the alkali metal sulfonate a co-solvent such as dimethylformamide. This is probably because at cathode voltages at which the hydrodimerization takes place, the alkali metal salts are also affected. Particularly when solutions containing the alkali metal sulfonates are stirred, the cathodic voltage necessary for hydrodimerization results also in discharging some alkali metal ions. Owing to the presence of these resulting metals, a chemical path is taken which results also in formation of the saturated monomer, rather than the hydrodimerization product. In the case of acrylonitrile, for example, propionitrile is also obtained as by-product. This probably occurs by 1,4- or 1,2-addition of the alkali metal ion to the acrylonitrile and decomposition by water of the resulting addition product to give the propionitrile. Whereas, according to the presently provided process, the two competing reactions i.e., the formation of hydrodimerization products versus formation of saturated monomer, can be manipulated to favor the hydrodimerization, nevertheless, some saturated monomer is formed when the electrolysis solution contains the alkali metal sulfonates rather than the tetraalkylammonium sulfonates, and the yield of hydrodimer is thereby decreased. On the other hand, purely chemical reaction does not take place when the tetraalkylammonium sulfonates are used instead of the alkali metal sulfonates. This is because at cathodic voltages which favor the hydrodimerization reaction, the tetraalkylammonium ion is not discharged. In the ease of acrylonitrile, for example, the optimum cathode voltage for conversion to the hydrodimerization product (adiponitrile) can vary from, say, about -1.8 to about 2.1 volts, as determined in a stirred run (versus the saturated calomel electrode). There is no lowering in yield of hydrodimerization product by chemical mediation such as that which occurs by use of the alkali metal sulfonates, for the tetraalkylammonium ion is not discharged at the operating voltage. For example, when a solution of acrylonitrile in aqueous tetraethylammonium p-toluenesulfonate is submitted to electrolysis, conversion of the acrylonitrile to adiponitrile occurs at about l.91 volts, whereas the tetraethylammonium ion is not discharged until about 2.5 cathodic volts. On the other hand, some olefinic compounds are hydrodimerized at less negative cathodic voltages, permitting suitable results to be obtained with salts of alkali metals. However, in order to insure against interfering reactions it is advantageous to employ salts of cations which have more strongly negative discharge potentials, e.g., more negative than -2.2 cathodic volts vs. the saturated calomel electrode. In the hydrodimerization of acrylonitrile it is definitely preferred that the conditions be such that. the cathode potential is no less negative than 1.7 volts (vs. the saturated calomel electrode).

Among the ammonium and amine sulfonates useful as electrolytes in the present invention are the alkyl, aralkyl, and heterocyclic amine and ammonium sulfonates, in which ordinarily the individual substituents on the nitrogen atom contain no more than 10 atoms, and usually the amine or ammonium radical contains from 3 to 20 carbon atoms. It will be understood, of course, that diand poly-amines and diand poly-ammonium radicals are operable and included by the terms amine and ammonium The sulfonate radical can be from aryl, alkyl, alkaryl or aralkyl sulfonic acids of various molecular weights up to for example 20 carbon atoms, preferably about 6 to 20 carbon atoms, and can include one, two or more sulfonate groups. Any of the quaternary ammonium sulfonates disclosed and claimed in my copending application S.N. 75,123 filed December 12, 1960, can suitably be employed.

Another especially suitable class of salts for use in the present invention are the alkysulfate salts such as methosulfate salts, particularly the amine and quaternary ammonium methosulfate salts. Methosulfate salts such as the methyltriethylam monium, tri-n-propylmethylammonium, triamylmethylammonium, tri-n-butylmethylammonium, etc., are very hygroscopic, and the tri-n-butylmethylammonium in particular forms very concentrated aqueous solutions which dissolve large amounts of organic materials. In general the amine and ammonium cations suitable for use in the alkylsulfate salts are the same as those for the sulfonates. Any of the quaternary ammonium alkyl. sulfates, such -as tetraethylammonium ethylsulfate, disclosed as suitable for such use in my copending application S. N. 147,070 filed October 23, 1961 can be utilized.

Various other cations are suitable for use in the present invention, e.g., tetraalkylphosphonium and trialkylsulfonium cations, particularly as sulfonate salts formed from sulfonic acids as described above, or as methosulfate salts.

As a further illustration of electrolytes suitable for use in the present invention, the following named salts were all successfully employed in hydrodimerizing acrylonitrile to obtain adiponitrile as the major product with little or no formation of impurities, generally employing concentrated aqueous solutions of the salts containing at least 15% and usually 20 to 40% :by weight acrylonitrile, and utilizing the general procedures of the illustrative examples herein:

(1) N trimethyl-N-trimethylethylenediammonium dip-toluenesulfonate (2) Benzyltrimethylammonium p-toluenes-ulfonate (3) Methyltri-n-butylphosphonium p-toluenesulfonate .(4) Tetraethylammonium sulfate (5) Di-tetraethyla-mmonium benzenephosph-onate (6) Trimethylsulfonium p-toluenesulfonate (7) Methyltri-n-hexylammonium p-toluenesulfo-nate (8) Benzyltrimethylammonium phosphate.

(9) Benzyltrimethylammonium acetate (10), Methyltri-n-butylammonium methosulfate 1 l) Benzyltrimethylammonium benzoate (12) Tetraethylammonium methanesulfonate (13) Benzyltrimethylammonium 2-naphthalenesulfonate (14): Bis-benzyltrimethylammonium rn-oenzenedisulfonate v 15) Benzyltr-imethylammonium thiocyanate (l6) Tetramethylammonium methosulfate acid :salts, benzoates, phosph-onates, etc., specifically, for

example','tetramethyl ammonium bromide, tetraethyl ammonium'bromide, tetramethylammonium chloride, tetraalkyl-phosphonium chloride, tetraethyl ammonium phosaisaasr on-a copper screen can thus be employed. The cathode,

which may be mercury, lead; or another metal, and the porous cup, if one is employed, are submerged in the solution of alpha,beta-olefinic nitrile in the concentrated aqueous salt or a mixture of the same with 'a polar solvent.

phate, etc.; and similarly the alkali, alkaline earth and other metal salts with the foregoing anions can be employed, e. g., sodium chloride, potassium phosphates, so-

dium acetate, calcium acetate, lithium :benzoate, calcium chloride, rubidium bromide, magnesium, chloride, as'well as the sulfonic acid, particularly aromatic sulfonic acid, and alkylsulfuri-c acid salts of the foregoing cations and of other alkali, alkaline earth, rare earth and other metals, e. g., cesium, cerium, lanthanum, yttrium, particularly with anions to achieve suficient'water solubility; The aluminum cation is only somewhat inferior to sodium in 'respect to its discharge potential, but most salts of aluminum tend to hydrolyze in water and precipitate aluminum oxide. herein ascontaining salts, electrolytesyeto, in specified amounts have reference to solutions containing salts suffi- It is understood that the solutions designated,

ciently stable to remaintin solution. w It will be recognized that'many cations are capable ofexisting in several valence states, and some valence, states will be more suitable as supporting electrolytes than others. Other examples of'sal-ts which can be employed in the present process, 211-, though not necessarily with equivalent or optimum results,

are barium bromide, barium acetate, barium propionate,

barium adipate, cerium sulfate, cesium chloride, cesium benzoate, cesium benzenesulfonate, potassium oxalate, potassiumsulfate, potassium ethyl sulfate, lananum acetate,

' lanthanium benzene sulfonate, sodium sulfate, sodium potassium sulfate, strontium acetate, rubidium sulfate, rubidium benzoate, trisodium phosphate, sodium hydrogen phosphate and sodium bicarbonate.

Solubility will to some extent set an upper limit on salt concentration in the electrolyte solution, although if considered on the basis of water solubility in the salt, fairly low concentrations of water can be employed, but n gen' eral there will be at least 5% or so by weight of water or other proton don-or present to avoid excess-iveproduction of higher polymeric materials, and water will generally constitute more than 15, or 20% by weight of the cathe olyte.

a lab-oratory scale, the following procedure and apparatus In conducting the electrolysis process batch-wise and ori may be employed. The-electrolytic cell will comprise a a container of material capable of resisting the action of the electrolytes, e. g., glass. 7 ing to divide it into an anode compartment and a cathode compartment may be a diaphragm 'in the form of a porous cup, e. g., of un glazed porcelain. The anode, which can be of, e. g., platinum or carbon, or any electrode'which is inert under the reaction conditions, is immersedin an Within the container, and serv anolyte contained. in the porous cup. The .an-olyte 'is an aqueous solution ofthe salt. When therelis employed no diaphragm in the. cell, stirring can be employed for 'pH control. Thereby the anode is subjected to little or The entirecell may be cooled by a jacket containing a coolant, and both the anode and cathode chambers may be equipped with condensers. However, aswill be hereinafter shown, the increase ofternperature which is produced during electrolysis generally does not result in so much of a decrease in yield that cooling other than with circulating water is economically required, Generally, the electrolysis'can, for example, be conducted at a temperature of from, say,'less than about 10 C. and up to almost the refluxing temperature of .the electrolytic bath and at higher temperatures under pressure. Actually, .slightly higher than ordinary ambient temperatures are conducive to improved yields, higher nitrile solubilities and lowered electrical resistance. This is to some extent counterbalanced by the tendency of some diaphragm materials to deteriorate at elevated temperatures, say of 70 C. or the like, and the tendency of acrylonitrile to vaporize at higher temperatures. In the hydrodimerization of acrylonitrile there is a'definite' advantage to operating in the range of about 40 to about 60 C., particularly about to C. Stirring of the solution during the electrolyses, if desired, may be conducted by mechanical or magneticmean-s. During the electrolysis, the pH of the cathlolyte' may be controlled as hereinbefore described; The quantity of current which is supplied to the cell will Vary with the nature and quantity of the bath and of the electrodes and with the operating temperature, but will ordinarily be at a rate greater than'0.5.-amperesand in the order of ,a current density of, say, from 2.0 to 20.0 or 40 or more amperes/dm. (d-m. refers to the area in square decimeters of cathode surface). The efiiciency of the process is, to some extent, dependent on the current density used. Thus for the eflicient production of adiponitrile, using a mercury cathode, it has been found that the current density shouldbe at least about 5 amperes/dm. and practical production rates ordinarily require the use ofmuch higher current densities.

It is important to note that the present process involves an actual electrochemical reduction in which an electure is neutralized and, after dilution, the organic phase is separated by decanting and/ or solvent extraction. After removing any residual inorganic matter by washing with water, the organic material is distilled to removersolvent andfto' give as residue the hydrodimerization product and any unconverted olefinic nitrile, together with by-products, if any. These may be separated from each other, e.g., by fractional distillation, etc. In experimental runs, results of the electrolysis can be conveniently arrived at, when the products are liquid, simply by analytical determination of thehydr'odimerization product and of the unconsumed monomer, if any,'e.g., by vapor phase chromatography.

The following equations are illustrative of the proposed mechanism of the process of the present invention which occurs under non-acidic conditions at suitable cathodic potentials and suitable concentrations:

The proposed mechanism is in sharp contrast to the free radical mechanism which presumably prevails in acid media to produce polymeric products from acrylic monomers.

V aerylonitrile polyacrylonitrile and to that which produces pinacols from ketones It will be noted that the proposed mechanism to adiponitrile avoids the free radical V, as would appear essential for any mechanism to have validity in view of the known propensity of acrylonitrile to polymerize in the presence of tration. For if the ion H encounters a high concentration of water molecules, rather than acrylonitrile molecules, it will take up two hydrogen ions from the water to form propionitrile; thus it is necessary to maintain a high acrylonitrile concentration to avoid or minimize this simple reducton. Similarly, hydrogen ions present under acidic conditions enter into an interfering reaction with ion II by adding to II to form propionitrile. While water molecules can interfere, some water or other source of proton donor is necessary to provide hydrogen to convert III to adiponitrile and avoid a tendency toward polymerization. Thus the catholyte will ordinarily comprise by weight or more water, although even a few percentage points of water is ordinarily sufficient. Of course, a certain minimum of water is advantageous in lowering electrical resistance.

The applicant does not intend to be limited to any particular mechanism, as the demonstrated results are obtained regardless of the mechanism advanced in explanation thereof. It is also to be understood that other electronic formulae for acrylonitrile may be substituted for I above:

E11 I CzCnCuN:

The proposed mechanism will aid in understanding the process and in explaining the significance of certain departures from the prior art and of certain requirements for the process.

It is desirable to avoid acidity in order to etfect the process of the present invention, both because of interfering polymerization reactions which occur in acidic media, and because of the discharge of hydrogen ions which occurs circa 1.5 volts. If only a small amount of hydrogen ions are present at the start of electrolysis, it may be simple to electrolytically discharge such ions at the cathode until the pH goes over 7 and then to proceed with the hydrodimerization while maintaining alkaline conditions.

The invention is further illustrated by, but not limited to, the following examples:

EXAMPLE 1 Tetraethylammonium p-toluenesulfonate was prepared as follows: A mixture consisting of 200 g. (1 mole) of ethyl p-toluenesulfonate, 101 g. (1 mole) of triethylamine and ml. of absolute alcohol was stirred at room temperature for 3.5 hours and then heated to 72 C. within 40 minutes. At this point an exothermic reaction occurred, and extraneous heating was discontinued and the mixture allowed to stand for 30 minutes. At the end of that time it was heated to reflux, and refluxing was continued for 6 hours. After being allowed to cool to room temperature, the solvents and any unreacted material was stripped off with an aspirator to obtain a residue which solidified. This was washed with absolute ether three times by decantation. After removing traces of solvent from the washed product with an aspirator, there was obtained as residue 296.8 g. of the substantially pure tetraethylammonium p-toluenesulfonate, M.P. 103104 C.

' Alundum cup containing, as anolyte, 30 ml. of said concentrated aqueous solution of the tetraethylammonium p-toluenesulfonate and immersed into a jacketed glass vessel containing the catholyte and ml. of mercury as cathode. An electric current was then passed through the resulting cell for three hours at about 2.3 amperes for the first hour, about 3.2 amperes for the second hour, about 3.4 amperes for the third hour, and an of 19.0 to 17.3 volts for the first hour and from 17.30 to 17.0 for the next two hours. At the end of the three-hour period an electric current of 3.5 amperes was passed into the cell for an additional 30 minutes. The electrolysis was thus conducted at from 5.5 to 6.2 amps/dm. and a total of 10.1 amp-hrs. The temperature of the catholyte was maintained at 20.5 C. to 26 C. by employing a mixture of acetone and Dry Ice in the cooling jacket. During the electrolysis, a total of 3.0 ml. of glacial acetic acid was added to the catholyte to maintain the pH thereof just alkaline to phenol red. I

After the electrolysis, the catholyte was extracted 6 times with 50 ml. portions of methylene chloride and the solvents stripped off to give 139.1 g. of concentrate. A 10% aliquot of the concentrate was removed for vapor phase chromatography, and the remainder of the concentrate was stripped by aspirator on the Water-bath to resolution. centration of acrylonitrile, based on the total weight of the V on unrecovered acryloni-trile. the concentrated aqueous tetraethylammonium p-toluenesulfonate lowering the concentration of acrylonitrile in the isnsaser chromatography it was ascertained that 29.8 g. of the initially employed acrylonitriie had been consumed to give 22.8 g. of adiponitrile; i.e'., theadiponitrile was obtained in a 75.2% theoretical yield. Neither propionitrile no bis(2-cyanoethyl)ether had been formed. 7

EXAMPLE 2 'g. of the sulfonate in 215 g. of water. The 73.3% solution thus obtained was used: for the hydrodimerization of 'acrylonitrile as followers:

j The catholyte was prepared by adding 33' g. of Water and 94.5 g. of acrylonitrile to 108' g. of the. above 73.3%

There was thus obtained a 40% weight concatholyte; The anolyte 'was prepared by adding 20 ml'. of water to 20 ml. of said 73.3% solution of sulfonate. Employing the apparatus and electrodes described in Ex- 7 ample 1, but using the :above 'catholyte and anolyte, an

electric current was passed through the cell for a period of 7 hours at an average current of 2.0-3.2 amps; (a total i 22.3 amp-hrs.) and an of from 19 to 18 volts during about the firstjfo ur and from:17.9 -17.0 'volts' during the last 6-hours. A 100% current .etficiency was determined by copper coulombmeter, measurement. During the first hours a total of 4.40 ml. of glacial acetic acid was intermittently added to the catholyte in order to maintain it just alkaline to phenol red, an'd the temperature of the catholyte was maintained at 23 C. to 25 C. by

means of the cooling-jacket which'formed p art of the cell container. V I

At the end of the 7 hour period, the catholyte Was neutralized; diluted with water, extracted ten times with carbonate. The dried product-was stripped of the meth ylene dichloride through a'Todd column and subsequent aspiration. Analysis of the concentrate by vapor phase chromatography showed that 50%v of the acrylonitrile had been consumed to give a 100% yield of adiponitrile based on the unrecovered acrylonitrile.

EXAMPLE 3 In order to determine the effect of acrylonitrile concentration onhydrodimerization, the procedure o f Example 1 was substantially repeated, except that instead of using .a catholyte containing a 40% concentration of acrylonitrile, as in Example 1, there were employed catholytes of fonate to 215 g, of water. there was then added 48 g; of water and 53.0 g. (1 mole) of acrylonitrile to give a catholyte having :a 20% by catholyte from 40% to 20% results in the formation of propi-onitrile, but only in a 'very low amount, When the experiment of this example was substantially repeated, but using only a 5%' concentration of acrylonitrile in theinitial catholyte, therewas obtained instead of the 99:1 adiponitrile to propionitrile ratio, only a A concentrated, aqueous solution of tetraethylammd',

nium p-toluenesulfonate was prepared by dissolving 586.7

1.68:1 ratio of adiponitrile to propionitrile, i.e., more than a third of the product was propionitrile. However, when the concentr-ationiof acryloni-trile was increased to 10% and the electrolysis was repeated, the ratio of adiponitrile to propionitrile-was very significantly increased, there being obtained about 8 times as much adiponitrile .a-s propionitrile. For the production of adiponitrile by the hydrodimerization -of acrylonitrile -it is therefore recommended that in order to avoid the large stockpiles of pripionitrile, the concentration'of the acrylonitrile in the'catholyte be at least"10% by weight of the total 7 weight of the catholyte.

passed through a cell having a' mercury (110 ml.) cathode, a platinum wire electrode which was held in an Alundum -cup, which cup'contained as anolyte ml. of 75% by weight aqueous tetraethylammonium. p-t-oluenesulfonate plus 20 ml. of water, and which clip was immersed in a catholytefconsisting of 93 g. of methacry lonitrile, 93 g. of said 75% aqueous sulfonate and 37.2 g. of dimethylformamide. During the electrolysis,-the temperature of the catholyte was maintained at 22-29 C. by

' jacket-c'oo-lingand the pH ofthe 'catholyte was kept just V ml. portions of methylene. chloride, washed three'times with 25 ml. portions of water and. dried over potassium alkaline to phenol red by intermittent addition to the catholyte of a total of 4.7 ml. of glacial acetic acid. During the filStfhOlll of operationtheEMLRwas from a high of 34 volts to a low of 23.9 volts. This decreased, during the subsequent 2 hours, to 19.0 volts and remainedat this value during the final 2 hours. Measurement of the cathode voltage versus a saturated calomel electrode gave values of from l'.98 to +2.05. A total of 12.3 amp-hrs. wa used, the average current being about 2.3 amps. for. the first hour and remaining constant at 2.5 amps. during the remaining 4 hours.

At the end of the electrolysis the catholyte was repeatedly extracted with methylene chloride, washed with water, dried and concentrated to remove the methylene chloride A 10% aliquot of the concentrate was removed for vapor phase chromatographic analysis; The residue was aspirated andsthen vacuum distilled to give .a mixture of dl and meso-Z,S-dimethyladiponitrile, B.P. 110 C./0.4 mm. and 116 C./0.7 5 mm., n

' 1.4327. Analysis of said, aliquot showed that 24.4 g. of

weight concentration of acrylonitrile based on. the total.

weight of catholyte. As anolyte there was employed 20 ml; of the 73.3% sulfonate solution plus 20 ml. of water. The apparatus and electrodes were in Example 1.' Electric current was passed through the cell for 3 hours, at an of 19.6 to 17.5 .and a total of 11.1 amp-hrs, while maintaining the temperature at 23.5-- 25.5 C. and intermittently'adding a total of 3.4 ml.-.

of glacial acetic acid to the'catholyte'in order to maintain the pH thereof just alkaline to phenol red.

'After electrolysis, the catholyte' was extracted with methylene dichloride, washed with water, dried'over m methacrylonitr-ile had been consumed. Hence'based on the unrecovered methacrylonitrile, the 18.7 g. yield of the 2,S-diniethyladiponitrile which was obtained represents a 75.3% theoretical yield.

EXAMPLE 5 V raining; an anolyte consisting of 40 ml. of said salt solu- 'tion,;sai'd cup being completely immersed in a catholyte 7 salt solution.

consisting of 68 g. of acrylonitrile (a concentration of 20.8% by weight of the catholyteyand 259 g. of said During this time the temperature of the catholyte Was allowed to increase from 43 C. co-50 C. andthepH-of the catholyte was maintained just alkaline t0 phenol-phthalein 'by addition of glacial acetic acid.

Operation was conducted at a total of 10.3 amp-hrs.

(increasing from 4.2 to 7.4 amps.) and the decreased from 16.9 to 14.5 volts during the electrolysis.

When the current was discontinued the catholyte was extrated with seven 50 ml. portions of methylene chloride, washed, and dried, and the dried organic material concentrated to 100 ml. to give a product which by vaporphase chromatography was found to contain 8.95 g.of adiponitrile, 6.75 g. of propionitrile and 46.9 g. of acry-lonitrile. No bis(beta-cyanoethyl)ether was present. Based on the consumed acrylonitrile, the yield of adiponitrile represented 41.6% conversion to adiponitrile versus 30.8% conversion to propionitrile.

EXAMPLE 6 This example shows the use of a lead cathode in the h drodimerization of acrylonitrile to adiponitrile.

A hollow perforated cylinder of lead was immersed in a catholyte consisting of 94.5 g. of acrylonitrile, 108 g. of a 56% aqueous solution of tetraethylammonium ptoluenesulfonate plus 33 g. of water to give a submerged surface area of about 240 c1n. An anode comprising a loop of platinum wire was placed in an anolyte consisting of 20 ml. of said 56% sulfonate solution plus ml. of water and contained in a porous, porcelain cup which was also immersed in said catholyte. An electric current was passed through the resulting cell at a cell voltage of 1719 volts and a total of 10.9 amp-hrs. for a period of 1.5 hours. During this time, the pH of the catholyte was maintained just alkaline by introduction of acetic acid. The catholyte was then extracted with seven 40 ml. portions of methylene chloride, and the extracts were washed with water, and then dried over potassium carbonate. After filtering the dried material the filtrate was concentrated for removal of methylene chloride. Vapor phase chromatographic analysis showed the presence of 69.5 g. of acrylonitrile, no propionitrile, and 22.5 g. of adiponitrile. Based on the consumed acrylonitrile, there was thus obtained an 88.4% yield of adiponitrile.

EXAMPLE 7 In a series of parallel runs, there was compared the efiicacy of sodium, potassium and lithium p-toluenesulfomates for use in the electrolytic hydrodimerization of acrylonitrile.

In each case there was employed a mercury cathode and a platinum wire electrode. The three different electrolytes each consisted of 380 g. of a saturated, aqueous solution of one of the alkali metal sulfonates and 47.5 g. (13.3% by weight of the electrolyte) of acrylonitrile. The electrolysis was conducted over 3-hour periods by passing an electric current through the cell, in each case, at an average of 5.5 arnps./dm. and, in each case, a total of 9.0 amp-hrs. The temperature was maintained at 2326 C. in all three cells.

After terminating the electrolyses, the electrolyte solutions were respectively extracted with methylene chloride, employing in each case seven 50 ml. portions of the chloride, and the extracts were respectively washed, dried and concentrated to 100 ml. Vapor phase chromatographic analyses showed the presence of substantial quantities of adiponitrile in each of the concentrates.

EXAMPLE 8 The triethylamine salt of p-toluenesulfonic acid was employed in the electrolytic hydrodimerization of acrylonitrile as follows:

A concentrated aqueous solution of the salt prepared by mixing together 95 g. of p-toluenesulfonic acid monohydrate, 35 g. of water, 51 g. of triethylamine (calculated for salt-formation) and a slight excess of the amine to bring the pH of the solution to 9.2. For the catholyte, 160 ml. of this solution was used with 120 g. of acrylonitrile. The anolyte, in which a platinum wire loop was immersed as anode, consisted of 25 ml. of the solution plus ml. of water. The anolyte and anode were conof methylene chloride.

18 tained in a porous, porcelain cup which was immersed to the top edge thereof, in the catholyte. Mercury (110 ml.) was employed as cathode.

Passage of an electric current through the cell was conducted for 9 hours at from 1.5 to 3.6 amps./dm. and a total of 14.5 amp-hrs. At the end of that time the catholyte, which by now had a pH of 9.4, was transferred from the cell and brought to ca. pH 6 by addition of aqueous hydrochloric acid. Hydroquinone was then added as stabilizer, and the whole was steam-distilled to remove any acrylonitrile and propionitrile. The residual liquid was then filtered and extracted twice with ether. The aqueous solution after ether extraction was then extracted five times with chloroform, and the extracts dried overnight over potassium carbonate. After stripping the chloroform from the dried product, the residue was distilled to give a fraction, B.P. 126146 C./4 mm., n 1.4377, which was shown by infra-red analysis to comprise adipo nitrile.

EXAMPLE 9 This example shows the use of a tin cathode in electrolytic hydrodimerization.

The cathode which was used was a tin hollow cylinder having a surface area of 243 cm. and being 2.75" in length and having an internal diameter of 7.00 cm. and an outer diameter of 7.45 cm., perforated with 10 holes at the bottom periphery and 6 holes at the upper periphery thereof (diameter of each hole: 0.954 cm.). It was immersed in a catholyte consisting of 60 g. of acrylonitrile and 227 g. of a saturated, aqueous solution of an equimolar mixture of sodium and potassium p-toluenesulfonate. A porous, porcelain cup containing a platinum anode and 40 ml. of said saturated solution as anolyte was also placed in the catholyte. Electric current was passed through the resulting cell for about 1.5 hours at a total of 12 amp-hrs. and a cell voltage which decreased from 16 to 13.2 volts. During the electrolysis, glacial acetic acid (7.8 ml.) was added to maintain the catholyte just alkaline to phenol phthalein and the temperature was maintained at 24-29 by jacket-cooling. The catholyte was then transferred and extracted with seven ml. portions After drying the extracts over potassium carbonate and concentrating to remove the solvent, there was obtained a residue which was shown by vapor phase chromatographic analysis to contain a substantial quantity of adiponitrile together with propionitrile and unreacted acryloni-trile.

EXAMPLE 10 A hollow cylinder of cadmium, having the dimensions and perforations described for the tin cathode of Example 9, was employed as cathode in the hydrodimerization of acrylonitrile. The catholyte and the anolyte were the same as those used in Example 9. The electrolysis was conducted for 1.5 hours at a cell voltage which decreased from 17.8 to 14.0 volts and at a total of 11.5 amp-hrs. The temperature of the catholyte during this time was kept at 23-27 C. by jacket-cooling, and the pH of the catholyte was maintained just alkaline to phenol-phthalein by continuous addition of a total of 7.6 ml. of acetic acid.

When electrolysis was discontinued, the catholyte was extracted with seven 50 ml. portions of methlyene chloride, and the extracts were evaporated on the water-bath. Vacuum distillation of the residue gave the substantially pure adiponitrile, B.P. 127 C./1.4 mm. or 130 C./l.5 mm., n 1.4378.

EXAMPLE 11 This example describes the electrolytic hydrodimerization' of crotononitrile.

During a period of 5 hours an electric current was' passed through a cell containing ml. of mercury as cathode and a platinum anode in a porous porcelain cup containing as anolyte 20 ml. of a 75% aqueous tetraethylammonium p-toluenesulfonate solution plus 20 ml.

159 of water, saidcup being completely immersed in a catholy-te consisting of 97.4 g. of said 75% solution of the sulfonate, and 38.2 g. of dimethylformamide; During this period the temperature of the catholyte was maintained at from 2026 C. and the pHof the catholytewas maintained just alkaline t-o phenol red by addition thereto of a total of 4.55 ml. of glacial acetic acid at intervals during the electrolysis. The operation wasconducted for a total of about 14.7 amp-hrs a cell voltage of from 22.8 to 33.0 volts and a cathode voltage as determined against the saturated calornel electrode of from 2.00 volts to -2.11 volts. V I

When the current was discontinued, the catholyte was repeatedly extracted with methylenedichloride, the extracts were washed and dried, and the dried material was cone t't t d t 1. 5 g-' I Vapor phase chromatographic analysis of the concent'rate showed that itlcontain fid 32.8 g. of 3,4-dimethyladiponi-trile and 62.0 g. of unreacted crotononitrile. Based on the unrecovered crotononitrile, the yield of hydro dimerization product represented 93% of theory.

EXAMPLE 12 Employing the. a paratus and the electrodes described in Example 11 3,B-diniethylacrylonitrile'was submitted to electrolytic hydrodimerilzation. The catholyte consisted of 105.0 g. of the dimethylacrylonitrile; 105.6 g. of a75 aqueous solution of tetraethylamrnonium p-toluenea sulfonate and 26.7 g. of dimethylformamide. The anolyte consisted of 20. mlfiof said 75 aqueous solution of sulfona te: plus 20 ml. of water. The electrolysis was conducted over a period of 5 hours for atotal of about 15.6 amp-hrs. and a cathode volt-age as determined against the saturated calomel electrode of from .-1 .72 to +2.23. D i the ec e y iis he temper ure or the catholy was maintained at from 23-26 C. by jacket-cooling, and the pH of the catholyte was maintained just alkaline to phenol red by intermittent addition of 'a total of 3.25 ml.

of glacial acetic acid' during'the electrolysis.

When the electrolysiswas completed, the catholyte was transferred with water to a separator'y funnel and the organic layer which formed was extracted with methylene chloride and back-washed with water, After drying the extracts overnight over anhydrous potassium carbonate and filtering, ith e filtrate was stripped of the methylene chloride to obtain 140.2 g. of concentrate. It Was dis: tilled with aspirator to remove volatiles. The residue which solidified upon cooling was washed with hexane and s tfllli ed from. abs ute al oh t get the su st n y pure 3,3,4,4-tetramethyladiponitrile, M.P. 133 C., which analyzed as. follows: i

Found Calcd. for

C1oH1a 2 Percent o ..Q 73. 24 73. 12 Percent H 10. 23 9. 82 lercent N .j. I 17.35 V 17. 05

Infra-red analysis further confirmed this structure. Crjyoscopic molecular weight determination gave a value of 1 67 as against 1 64.25, the calculated value.

EXAMPLE 13 completely immersed in a catholyte consisting of 92.0 g. of an 89% aqueous solution of the sulfonate, 100 g. of acrylonitrile and 43 g. of water. The concentration of acrylonitrile dissolved in the catholyte was 42.5%. During this period the temperature of the catholyte was maintained at from 20-26 C. and the pH of the catholyte was maintained just alkaline to phenol red by intermittent addition of a total of 2.55 ml. of glacial acetic acid. The operation was conducted for a total of about 9.0 amp-hrs, a cell voltage of 36.5 to 23.0 volts and a cathode voltage as determined against the saturated calomel electrode of from 1.55 to -1.85.

When the current was discontinued, the catholyte was neutralized with acetic acid, and then extracted 4 times with ml. portions of methlyene-dichloride. The extracts were washed with water, dried, and stripped of methylenedichloride to give the substantially pure adiponitrile as residue.

EXAMPLE 1 4 An ammonium salt was prepared-by reacting tributylamine with dimethyl sulfate as "follows: A flask was charged with 74 grams of the amine and 50 ml. alcohol and 50 grams dimethyl sulfate in 50 ml. alcohol was added while the flask was cooled in an ice bath. After the reaction-mixture was stirred for about an hour with cooling, it was permitit d to stand at room temperature for several days, and the. salt product was then purified by successive aspirations with heat over a water bath and washings with ether. The soft, crystalline methyltributylammonium methosulfate product weighed 129.6 grams (of which about5 grams was probably water). A 125.6 'gram amount of the product Was dissolved in 14.4 grams water to give a salt solution of 89.6% concentration. A 5.12 gram amount or this salt solution dissolves more than 6.25 grams acrylonitrile, for a greater than concentration of acrylonitrile. A dilution of 1.15 grams water caused no. phase separation, demonstrating that a 73% salt solution could be used to prepare a 50% acrylonitrile solution. A 5.07 gram amount of the salt solution dissolved at least 5.0 gram nitrobenzene and. addition of water demonstrated that a 76% salt solution could dissolve. at least. 45 6% nitrobenzene.

To hydrodirnerize acrylonitrile a catholyte was prepared from 63.6 grams of the 89.6% methyltributylamnonium methosulfate solution, 77.6 grams acrylonitrile,

and 14.3 grams water, and employed in a cell with an anolyte 12 ml. 76% nrethyltriethylamrnonium p-toluenesulfon'ate in water and 12 ml. water. The initial. pH of the catholyte was adjusted to neutrality by addition of a very smallamount of a 40% aqueous solution of benzyltrlmethylammonium hydroxide and a total of 1.95 ml.

aceticacid was added during electrolysis to insure that only slight alkalinity developed. The electrolysis was conducted as a current of 3 amperes. for about 3 hours (9 ampererhours) at cathodic voltages of 1.87 to 1.89. The adiponitrile product, was isolated in the usual manner.

EXAMPLE 15 Tributylphosphine and methyl p-toluenesulfonate were reacted in mole/mole ratio in alcoholic solution with cooling to maintain temperature lower than 30 C., and volatile materials were then stripped by aspiration over a water bath and the residual, syrup was washed with anhydrous other. A sample of the syrup, methyltri-n-butylphosphonium p-toluenesulfonate, crystallized upon standing. An 80% by weight concentration of the syrup in water appeared miscible with acrylonitrile. For hydrodimerization, about ml. catholyte was preparedfrom 61 grams of the 80% phosphonium salt solution, 91.3 grams acrylonitrile and a traceof p -ni trosodimet hylaniline. As anolyte, 10 ml. 80% tetraethylarnmonium -p-toluenes-ulr"0nate was diluted with 10ml. water. At the start of the'electrolysis, hydrogen evolution indicated a slight amount of acidity in the salt solution which was discharged in about three minutes at cathodic voltages of 1.45 to -1.69 and current of 1 to 2.8 amperes; when the pH became greater than 7, the hydrodimerization was conducted at cathodic voltages of 1.89 to 1.90 and 3 amperes current for three hours, with addition of a total of 2.55 ml. acetic acid. Treatment of the product in the usual way produced 60 ml. of residual material, from which 11.5 grams adiponitrile was distilled. Apparently preferential extraction of the phosphonium salt by acrylonitrile caused the presence of large amounts of salt in the residual liquid, and the distillation was therefore employed to obtain the adiponitrile. The phosphonium salts, reported to have cathodic discharge potentials of -2.2 to -23 volts (vs. standard calornel electrode) are thus demonstrated to be suitable for hydrodimerizing olefinic compounds in accordance with the present invention.

EXAMPLE 16 A continuous procedure for hydrodimerization of acrylonitrile'was conducted in a cell in which lead plates separated by a membrane were used for cathode and anode and the gap between the plates was less than onehalf inch. The cell was provided with pumping means to separately circulate the anolyte and Catholyte past their respective electrodes, and with means for continuously adding acrylonitrile and means for separating the adiponitrile product from the Catholyte and recycling the Catholyte. Dilute mineral acid was employed as anolyte and the catholyte, as charged, was 17.6% by weight acrylonitrile, 37.2% by weight water and 42.2% by weight tetramethylammonium toluenesulionate. The hydrodirnerization was conducted at a Catholyte linear rate of circulation past the cathode of 1.2 ft./sec., current density of 20 amperes/dmF, and at a pH of 8.59.0. The yield of adiponitrile based on acrylonitrile consumed was 90% and the yield oi'propionitr'ile was only 1%. Such yields were obtainable on conducting the hydrodimerization on a continuous basis for a matter of days or weeks.

' The current through the cell was of the order of amperes, but even much greater currents can be used by employing either higher current densities or greater electrode areas.

EXAMPLE 17 Similar runs to Example 16 were made at lower pHs with the results indicated below. In these runs, the acrylonitrile contained a small amount of p-methoxyphenol as polymerization inhibitor.

Table 1.-pH Efiect at constant conditions Catholyte pH Current density, ampsJdm. Catholyte recirculation rate, ft./see Catholyte feed composition:

Percent AN Percent H 0. Percent TMATS Cathode Current efiicieney based on ADN produced,

percent ADN yield based on AN consumed, percent PN yield, percent letramethylammoniinn toluenesulfonate (65% para, ortho).

the procedure was further complicated by polymerization of acrylonitrile.

EXAMPLE 18 Utilizing the procedure of Example 16, a hydrodimerization of acrylonitrile was conducted at a slightly higher than usual pH, viz. at 10.3, with results as follows:

01 {Estrumethylammonium toluenesulfonate (65% para, 35% While the yield of adiponitrile was fairly good, it will be noted that the amount of the unwanted propionitrile was considerably higher than in Example 16.

The above examples and data are illustrative of the hydrodimerization of alpha,beta-olefinic nitriles. Specific process conditions may vary, of course, with different cell structures, with ratio of volume of catholyte to surface area of cathode as well as with, other variables such as temperature, cathode voltage, current density, etc. Moreover, a number of cells can be combined into a single unit, and the process can be carried out continuously by means of a circulating pump whereby the catholyte is Withdrawn from the cell during the process, the hydro dimerization product is separated therefrom, and the residue is reintroduced into the cell together with -addi tional olefinic compound to make up the initial strength.

EXAMPLE 19 A catholyte solution containing 6% by weight acrylonitrile and 9.4% tetraethylammoniurn p-toluenesulfonate by weight was electrolyzed in a divided cell with addition of small increments of acetic acid to counteract alkalinity.

The yield of adiponitrile, based oncurrent consumption,

EXAMPLE 20 A catholyte containing 6% by weight of acrylonitrile and 5% by Weight NaCl was electrolyzed with addition of acetic acid as necessary to maintain the desired pH, a larger amount than usual being employed. The bulk of the product was propionitrile, but a very small amount of adiponitrile was also obtained.

EXAMPLE 21 A catholyte containing 6% by weight acrylonitrile and 5% by weight strontium chloride was electrolyzed with addition of acetic acid to counteract alkalinity. A 9.2% yield of adiponitrile, based on current consumption, was obtained.

The presently provided process provides a very simple and economical method for the manufacture of aliphatic polynitrile compounds, particularly the diand tetranitriles. The electrolytic process of this invention is advantageous in that, during the electrolysis, electrolyte is not consumed, only a minor proportion, if any, of the olefinic nitrile is converted to the saturated monomer and the electrolysis can be conducted if desired without the use of cost-increasing cooling systems and with highly efficient utilization of electric current.

The process of this invention is of especial interest for those instances in which the dior tetra-cyano alkanes have been obtainable only with difficulty or not at all by other processes. By hydrodimerizing, e.g. an olefinic nitrile, it often is possible to obtain, using the process of this invention, a branched parafiinic dinitrile more easily and more economically than otherwise would be possible. For example the alpha-alkylacrylonitriles, as shown in Example 5, are hydrodimerized to the 2,5-di-alkyladiponitriles. Thepositioning of the two alkyl groups in this instance is particularly important because superior resinoust products of the poly amide type are obtainable by reaction of dicarboxylic compounds with 2,5-dimethylhexamethylenediamine. The presently provided 2,5-dia ndipb'nitrne is easily converted by hydrogenation to the highly valuable 2,S-dimethylhexamethylene diaminq Thefparafiinic dinitrile s prepared by the present process and their hydrogenation products are generally useful in the manufacture of high-molecular weight condensation polymers, e.g., by reaction with dihydroxy or dicarboxylic compounds; and the tetra-functional compounds, as well as the difunctional compounds, are efiicient plasticizers for synthetic resins and plastics;

' nitrile selected from the group consisting of nitriles of the It is obvious that many variations may be made in the I process of this invention without departing from the spirit and scope thereof. i

What is claimed is: V

1. A method of producing hydrodimers of aliphatic alpha,beta-olefinic nitriles in substantial yield which comprises subjecting a solution of aliphatic alpha,beta-olefinic nitrile selected from the group consisting of nitriles of the formulae in which R, R and R" are selected from the group consisting of hydrogen and alkyl radicals of l to 5 carbon atoms to electrolysis by passing an electric current through said solution in contact with a cathode, causing development of the cathode potential required for hydrodimerization of the nitrile, the solution consisting essentially of water, more than about 5% by weight of the nitrile, and at least 5% by weight of supporting electrolyte, salt to make the solutionconductive, and recovering in substantial yield hydrodimer in which coupling has occurred between corresponding carbon atoms of two molecules of the starting nitrile, the said carbon atoms being in the beta-position of the .olefinic bond with respect to a nitrile group of the starting nitrile, the said hydrodimer having twice the carbon atoms of the starting nitrile, the said electrolysis being conducted in a cell in which both cathode and anode are in actual physical contact with electrolyte. t

2. The method of claim 1 in which the electrolysis is efiiciently conducted with agitation at a current density of greater than 10 amperes/ square decimeter of cathode surface in a cell in which the electrodes are no more than one-half inch apart.

3, The method of claim 1 in which the, electrolysis is carried to more than 50% conversion to the hydrodimer.

4. The method of claim 1 in which a divided cell is employed inv which the average nitrile concentration is gfaater than 15% by weight of the catholyte,

5. The method of claim 1 in which the pH in the bulk of the solution is in the range of about 6 to about 12 6 The method of claim 1 in which the salt provides a cation discharging at substantially more'negative cathode potentials than that at which the hydrodimerization of the nitrile occurs and the cathode employed has a hydrogen overvoltage greater than that of copper;

7. The method of .claim 1 in which a divided cell is employed and the catholyte is prevented from becoming in which R, R and R" are selected from the group consisting of hydrogen and alkyl radicals of 1 to 5 "carbon atoms to electrolysis by passing an electric current through said solution in a divided cell in contact with a cathode under substantially non-polymerizing conditions, causing development'of the cathode potential required for hydrodimerization of the nitrile, the solution comprising water, more than about 5% by weight of the nitrile and to make the solution conductive at least 5% by Weight of a supporting electrolyte salt which provides a cation discharging at cathode potentials more negative than that at which hydrodimerization of the nitrile occurs and more negative than that at which sodium discharges, and recovering in substantial yield hydrodimer having twice the car-,

bon atoms of the starting nitrile, the said electrolysis being conducted in a cell in which both cathode and anode'are in actual physical contact with electrolyte. v

9. The method of claim 8 in which the salt concentration constitutes more than 30% by weight of the salt and water present in said solution and in which the pH in the bulk of the solution is in the range of about 6 to l2.

10. The method of claim 1 in which the cathode is lead.

11. The method of claim '1 in which the nitrile is acrylonitrile and the supporting electrolyte salt is hydrotropic.

12. The method of claim 11 in which the hydrodimerization is conducted at a cathode potential no less negative than l.7 volts and a polar solvent is employed along with'water.

13. The method of claim 1 in which .a polymerization inhibitor is employed.

14. The method of claim 1 in which the aqueous electrolyte comprises a salt selected from the group consisting of amine and ammonium s ulfonates and alkylsulfates.

15. The method of claim 1' in which the hydrodimer product is recovered by extraction with a solvent therefor.

16. A method of producing adiponitrile in better than 50% yield from acrylonitrile which comprises subjecting an acrylonitrile solution to electrolysis by passing an electric current through said solution in contact with a cathode having an overvoltage greater than that of copper under substantially non-polymerizing conditions, the current density being greater than 10 amperes/ square decimeter of cathode surface, causing development of the cathode potential required for hydrodimerization of the acrylonitrile, the solution comprising water, more than 10% by weight of the acrylonitrile and supporting electrolyte .salt to make the solution conductive; the amount of salt' being above about 30% by weight of the total amount of salt and water present in said solution, the salt providing' a cation discharging at cathode potentials more negative than that at which the hydrodimer-ization of acrylonitrile occurs, and more negative than that at which sodium discharges, and obtaining adiponitrile in better than 50% yield.

17. The method ofclaim 16 in which the catholyte is p evented from becoming excessively alkaline by providing acid thereto to counteract the alkalinity developed at the cathode, and in which the temperature of the catholyte ismaintained in'the range of about 40 to about C.

25 18. A process for conducting the hydrodimerization of oL,fi-II1ODO-0l6fiIllC nitriles which comprises subjecting to electrolysis, in contact with a cathode having a hydrogen over-voltage greater than that of copper, a solution comprising water a nitrile selected from the group consisting of nitriles of the formulae (3N (EN in which R, R and R" are selected from the group consisting of hydrogen and alkyl radicals of 1 to 5 carbon atoms, and a salt selected from the class consisting of the saturated aliphatic and heterocyclic amine salts and the saturated aliphatic and heterocyclic quaternary ammonium salts of a sulfonic acid selected from the class consisting of aryl and alkaryl sulfonic acids wherein the total number of carbon atoms in the sulfonic acid is from 6 to 12 and the total number of carbon atoms in each of said amine and ammonium salt-forming radicals is from 4 to 20, the concentration of the olefinic nitrile in the solution being from about 10% to 50% by weight of the solution, the concentration of said salt in the solution being above about 30% by weight of the total amount of water and salt present in said solution and up to saturation, the pH of the solution being above 7 but below about 9.5, and the and 26 said electrolysis being conducted in a cell in which both cathode and anode are in actual physical contact with electrolyte.

19. The process of claim 18 in which the nitrile is acrylonitrile.

20. The method of claim 16 in which a divided cell is employed so that the acrylonitrile solution does not contact the anode.

21. The method of claim 16 in which a tetraalkylammonium alkylsulfate salt is used as electrolyte.

22. The method of claim 16 in which a tetraalkylammonium aromatic sulfonate salt is used as electrolyte.

23. The method of claim 16 in which the pH in the bulk of the solution is above 7 but below about 9.5.

References Cited by the Examiner UNITED STATES PATENTS 2,439,308 4/48 Leekley 260-290 2,575,553 11/51 Kolyoort 260-29.6 2,632,729 3/53 Woodman 204-72 2,726,204 12/55 Park et a1. 204-72 FOREIGN PATENTS 566,274 l1/58 Canada.

JOHN H. MACK, Primary Examiner.

WINSTON A. DOUGLAS, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,193,481 July 6, 1965 Manuel M. Baizer It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, lines 10 to 12, for the extreme right-hand portion of the formula reading CHR CHR read L column 5, line 41, for "excesive" read excessive column 6, line 6, for "eelctrolytic" read electrolytic column 7, line 59, for "cathods" read cathodes column 8, line 64, for "or", second occurrence, read of column 9, line 28, for "triethylethanolammonium" read trimethylethanolammonium column 13, formula (III) for the extreme righthand portion of the formula reading CH+20fi read CN+2OH' column 15, line 14, for "followers" read follows line 26, for "four" read hour column 16, line 16, for "pripionitrile" read propionitrile column 17, line 4, for "extrated" read extracted Signed and sealed this 7th day of June 1966.

(SEAL) Attest:

ERNESTd/V. SWIDER EDWARD J. BRENNER Attestlng Offlcel" Commissioner of Patents 

1. A METHOD OF PRODUCING HYDRODIMERS OF ALIPHATIC ALPHA, BETA-OLEFINIC NITRILES IN SUBSTANTIAL YIELD WHICH COMPRISES SUBJECTING A SOLUTION OF ALIPHATIC ALPHA, BETA-OLEFINIC NITRILE SELECTED FROM THE GROUP CONSISTING OF NITRILES OF THE FORMULAE 